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AP Biology Cell Communication and Homeostasis

AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

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Page 1: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Communication and

Homeostasis

Page 2: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Dynamic Homeostasis

Page 3: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

What is (dynamic) homeostasis?

Homeostasis = The property of a system that regulates its internal environment to maintain stable, (relatively) constant conditions In living things, often terms “dynamic

homeostasis” - what do you figure this indicates?

Page 4: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Feedback Control Homeostasis is often

maintained through the use of feedback systems (or loops).

A feedback system uses the consequences of the process (too much or too little produced) to regulate the rate at which the process occurs Consists of a sensor, a

control center, and an effector pathway

Page 5: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Positive vs Negative

Feedback loops may be positive or negative Negative feedback mechanism:

Maintains homeostasis by returning a changing condition back to its stable target point Discussion: although there are negative

and positive operons, both types are a negative feedback mechanism - why?

Page 6: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Generalized Negative Feedback Model

high

low

hormone 1

lowersbody condition

hormone 2

gland

specific body condition

raisesbody condition

gland

Page 7: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Controlling Body Temperature

high

low

nerve signals

sweat

nerve signals

body temperature(37°C)

shiver

dilates surfaceblood vessels

constricts surfaceblood vessels

Nervous System Control Feedback

hypothalamus

hypothalamus

Page 8: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

liver

pancreas

liver

Regulation of Blood Sugar

blood sugar level(90mg/100ml)

insulin

body cells takeup sugar

from blood

liver storesglycogen

reducesappetite

glucagon

pancreas

liver releasesglucose

triggershunger

high

low

FeedbackEndocrine System Control

islets of Langerhans beta islet cells

islets of Langerhansalpha islet cells

Page 9: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Positive vs Negative

Alterations in negative feedback mechanisms -> deleterious consequences

Discussion: People who are diabetic produce minimal insulin. What effect does this have on the blood sugar control feedback loop?

Page 10: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Positive vs Negative Positive feedback mechanism: Does

not maintain homeostasis; instead, amplifies responses and processes, moving the system further and further away from starting conditions. Example: labor in childbirth

Page 11: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Generalized Positive Feedback Model

high

hormone 1

raisesbody condition

gland

specific body condition

Or…

Page 12: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Generalized Positive Feedback Model

low

hormone 1

lowersbody condition

gland

specific body condition

Page 13: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Discussion Describe a positive feedback loop in the case of

asthma, taking into account variables such as: airway swelling/narrowing aiway irritation blood oxygen levels cortisol increasing heart & breathing rates lung oxygen content nervous system recognition of blood oxygen levels oxygen available to brain panic release of stress hormones such as cortisol

Page 14: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Maintaining Homeostasis The activities and stability of cells,

organisms, and also whole populations, communities, ecosystems etc. are affected by both biotic and abiotic factors Discussion: Think back through the course!

Can you come up with a biotic and abiotic factor that affects cell activities? Organism? Population or community?

AND, how does the cell/organism/population maintain homeostasis when that biotic or abiotic variable changes?

Page 15: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling

Page 16: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling Every feedback loop in an organism that we

discussed, positive or negative, has one thing in common: cell signaling.

In a multicellular (and even unicellular!) organism, recognizing and responding to changes, internal or external, necessitates cell-to-cell communication

Cells do this by generating, transmitting, and receiving chemical signals

Page 17: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell SignalingSignals can be

stimulatory…

or inhibitory.

Page 18: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling Cell signaling (sometimes just called

“signal transduction”) has three general stages: Reception Transduction Response

Page 19: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling - Reception RECEPTION

Signaling begins with the recognition of a chemical messenger by a receptor protein embedded in the cell membrane Chemical messenger = a ligand

Different receptors “recognize” different ligands due to fit, in a one-to-one relationship (think enzymes!)

Page 20: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling - Reception The ligand binding to the receptor

changes the receptor’s conformation (shape), which initiates the next step, transduction

Page 21: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling - Transduction Signal transduction is the process

by which a signal is converted to a cellular response.

The utility of signal transduction is signal amplification: through a cascade of chemical reactions, a single recognized ligand will be able to trigger a proportionally larger response

Page 22: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signal Transduction The receptor protein was an integral protein that

spanned the membrane When it changes conformation, the part of it

exposed to the cytoplasm changes conformation too

It does something new now in the cytoplasm, such as… Serving as an enzyme Opening up a channel between cell interior and exterior

(like ion channels in neurons!) Release a polypeptide from itself into the cytoplasm

…which is the first in what will be a series of chemical reactions, using a variety of second messengers inside the cell.

Page 23: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signal Transduction The end result of the signal cascade

could be producing or destroying transcription factors, activating enzymes, cytoskeleton rearrangement… and often many related results from the same signal!

http://bcs.whfreeman.com/thelifewire/content/chp15/15020.html

Page 24: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signal Transduction Signal transduction diagrams can

follow some slightly different conventions, but common ones are: A stimulates B A inhibits B Translocation/Relocation

B to C is a larger (amplified) response than A to B

A

A

A

B

B

B C

A

Page 25: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signal Transduction A and B subunits join to make C

A separates into subunits B and C

Multistep pathway from A to B with some steps not shown

B

B

B

A

A

A

C

C

Page 26: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Discussion Consider this very simple diagram of a

signal cascade (bigger image on next slide), and answer: What’s happening? What is the ligand?

What are the second messengers? Does EGF trigger or inhibit gene regulation?

Page 27: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Page 28: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signal Transduction That example displayed a common signal

transduction method: a phosphorylation cascade A series of protein kinases adding a phosphate

group to the next protein in the sequence (protein kinase = acts like an enzyme activator using ATP)

Reception

Transduction

Response

mRNANUCLEUS

Gene

P

Activetranscriptionfactor

InactivetranscriptionfactorDNA

Phosphorylationcascade

CYTOPLASM

ReceptorGrowth factor

Page 29: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Phosphorylation Cascade

Page 30: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell Signaling Specificity

Which receptors and secondary messengers a cell possesses determines which signals it will respond to, and how This is why a liver and a

heart cell will do two different things when activated by the same hormone, like epinephrin

Page 31: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Short-Distance Signaling: Nervous System

Page 32: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Discussion QUICK! NO NOTES!

What do you remember about how neurons signal each other??

Page 33: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cells have voltage! Opposite charges on opposite sides of

cell membrane membrane is polarized

negative inside; positive outside charge gradient stored energy (like a battery)

+ + + + + + + ++ + + + + + +

+ + + + + + + ++ + + + + + +

– – – – – – – ––– – – – –

– – – – – – – ––– – – – –

Page 34: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How does a nerve impulse travel? Stimulus: nerve is stimulated

reaches threshold potential open Na+ channels in cell membrane Na+ ions diffuse into cell

charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized

– + + + + + + ++ + + + + + +

– + + + + + + ++ + + + + + +

+ – – – – – – –– – – – – – –

+ – – – – – – –– – – – – – –Na+

Page 35: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Gate

+ –

+

+

channel closed

channel open

How does a nerve impulse travel? Wave: nerve impulse travels down neuron

change in charge opens next Na+ gates down the line “voltage-gated” channels

Na+ ions continue to diffuse into cell “wave” moves down neuron = action potential

– – + + + + + +– + + + + + +

– – + + + + + +– + + + + + +

+ + – – – – – –+ – – – – – –

+ + – – – – – –+ – – – – – –Na+

action potential

Page 36: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How does a nerve impulse travel? Re-set: 2nd wave travels down neuron

K+ channels open K+ channels open up more slowly than Na+ channels

K+ ions diffuse out of cell charges reverse back at that point

negative inside; positive outside

+ – – + + + + +– – + + + + +

+ – – + + + + +– – + + + + +

– + + – – – – –+ + – – – – –

– + + – – – – –+ + – – – – –Na+

K+

action potential

Page 37: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How does a nerve impulse travel? Combined waves travel down neuron

wave of opening ion channels moves down neuron signal moves in one direction

flow of K+ out of cell stops activation of Na+ channels in wrong direction

+ + – – + + + ++ – – + + + +

+ + – – + + + ++ – – + + + +

– – + + – – – –– + + – – – –

– – + + – – – –– + + – – – –Na+

action potential

K+

Page 38: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Synapse

Impulse has to jump the synapse! junction between neurons has to jump quickly from one cell to next

What happens at the end of the axon?

How does the wave

jump the gap?

Page 39: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

axon terminal

synaptic vesicles

muscle cell (fiber)

neurotransmitteracetylcholine (ACh)receptor protein

Ca++

synapse

action potential

Chemical synapse Events at synapse

action potential depolarizes membrane

opens Ca++ channels neurotransmitter vesicles

fuse with membrane, release neurotransmitter to synapse diffusion

neurotransmitter binds with protein receptor Ligand-gated ion channels

open neurotransmitter

degraded or reabsorbed

We switched…from an electrical signal

to a chemical signal

Page 40: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Nerve impulse in next neuron Post-synaptic neuron

triggers nerve impulse in next nerve cell Neurotransmitter = ligand opens ligand-gated ion channels Na+ diffuses into cell K+ diffuses out of cell

switch back to voltage-gated channel

– + + + + + + ++ + + + + + +

– + + + + + + ++ + + + + + +

+ – – – – – – –– – – – – – –

+ – – – – – – –– – – – – – –Na+

K+

K+K+

Na+ Na+

Na+

ion channel

binding site ACh

Here wego again!

Page 41: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Discussion How do neurons illustrate the basic principles

of signal transduction pathways?

“Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. Different receptors recognize different ligands, which can be peptides, small chemicals, or proteins, in a one-to-one relationship. A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal. Second messengers (hint: ions in this case) are often essential to the function of the cascade.”

Page 42: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Effects of Changes in Pathways Neurons illustrate what can happen when a

signaling pathway is tampered with!

SSRIs like Prozac and Zoloft block the channels that permit the presynaptic neuron to take the neurotransmitter serotonin back in.

Serotonin is used by neurons in the “happiness” pathways in the

brain. What’s the effect? Discuss using the terminology of cell

signaling.

Page 43: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology 2007-2008

Long-Distance Signaling:

Endocrine System

Page 44: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Why are hormones needed? chemical messages from one

body part to another communication needed to

coordinate whole body daily homeostasis & regulation of

large scale changes solute levels in blood

glucose, Ca++, salts, etc. metabolism growth development maturation reproduction

Regulation

growth hormones

Page 45: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Regulation & Communication Animals rely on 2 systems for regulation

endocrine system system of ductless glands

secrete chemical signals directly into blood chemical travels to target tissue target cells have receptor proteins slow, long-lasting response

nervous system system of neurons

transmits “electrical” signal & release neurotransmitters to target tissue

fast, short-lasting response

Page 46: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Nervous & Endocrine systems linked Hypothalamus = “master nerve control center”

nervous system receives information from nerves around body

about internal conditions releasing hormones: regulates release of hormones

from pituitary

Pituitary gland = “master gland” endocrine system secretes broad range

of “tropic” hormones regulating other glands in body

hypothalamus

pituitary

posterior

anterior

Page 47: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How do hormones act on target cells Lipid-based hormones

hydrophobic & lipid-soluble diffuse across cell membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors

turn on genes

Protein-based hormones hydrophilic & not lipid soluble

can’t diffuse across cell membrane bind to receptor proteins in cell membrane trigger secondary messenger pathway activate internal cellular response

enzyme action, uptake or secretion of molecules…

Page 48: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

nucleus

target cell

DNAmRNA

protein

blood

proteincarrier

S

S

S

S

Action of lipid (steroid) hormones

binds to receptor protein

cytoplasm

becomes transcription factor

ex: secreted protein = growth factor (hair, bone, muscle, gametes)

2

4

6

cross cell membrane

1

steroid hormone

mRNA read by ribosome5

plasma membrane

protein secreted7

3

Page 49: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Action of protein hormones

activatesenzyme

activatesenzyme

activates enzyme

ATP

produces an action

P1

2

3

cytoplasm

receptor protein

response

signal

secondarymessengersystem

signal-transduction pathway

acts as 2° messenger

target cell

plasma membrane

binds to receptor protein

proteinhormone

ATPactivatescytoplasmicsignal

cAMP

GTP

activatesG-protein

transduction

Page 50: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Effects of stress on a body

Spinal cord(cross section)

Nervesignals

Nervecell

Releasinghormone

Stress

Hypothalamus

Anterior pituitary

Blood vessel

ACTH

Adrenalgland

Kidney

adrenal medullasecretes epinephrine

& norepinephrineAdrenal cortexsecretesmineralocorticoids& glucocorticoids

(B) LONG-TERM STRESS RESPONSE(A) SHORT-TERM STRESS RESPONSE

Nerve cell

Effects of epinephrine and norepinephrine:

1. Glycogen broken down to glucose; increased blood glucose

2. Increased blood pressure3. Increased breathing rate4. Increased metabolic rate5. Change in blood flow patterns, leading

to increased alertness & decreased digestive & kidney activity

Effects of mineralocorticoids:

1. Retention of sodium ions & water by kidneys

2. Increased blood volume & blood pressure

Effects of glucocorticoids:

1. Proteins & fats broken down & converted to glucose, leading to increased blood glucose

2. Immune system suppressed

MEDULLA CORTEX

Page 51: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

adrenal gland

Ex: Action of epinephrine (adrenaline)

activatesprotein kinase-A

activatesglycogen phosphorylase

activates adenylyl cyclase

epinephrine

liver cell

releasedto blood

1

25

receptorproteinin cell membrane

cytoplasm

6glycogen

activatesphosphorylase kinase

GTP

cAMP

4

activatesG protein

ATP

glucose

activates GTP

3

signal

transduction

response7

GDP

http://bcs.whfreeman.com/thelifewire/content/chp15/15020.html

Page 52: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Benefits of a 2° messenger system

Amplification!

signal

receptor proteinActivated adenylyl cyclase

amplification

amplification

amplification

amplification

GTP G protein

product

enzyme

protein kinase

cAMP

Not yetactivated

1

2

4

35

6

7

FAST response!

amplification

Cascade multiplier!

Page 53: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology 2007-2008

Cell-to-Cell Signaling:Immune System

lymphocytesattackingcancer cell

phagocytic leukocyte

lymphsystem

Fighting theEnemy Within!

Page 54: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Why an immune system? Chemical defense against infections that disrupt

dynamic homeostasis! (Animals aren’t the only organisms with defenses but we’re focusing on us)

Attack from outside lots of organisms want you for lunch! among other advantages, like shelter & reproduction, animals are a

tasty nutrient- & vitamin-packed meal cells are packages of macromolecules

animals must defend themselves against invaders (pathogens) viruses - HIV, flu, cold, measles, chicken pox bacteria - pneumonia, meningitis, tuberculosis

Lyme disease Fungi - yeast (“Athlete’s foot”…) Protists - amoeba, malaria

Attack from inside cancers = abnormal body cells

Mmmmm,What’s in your

lunchbox?

Page 55: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Immune System

Immune defenses may be non-specific or specific Non-specific = broad, defends against

many kinds of attackers Specific = targets one kind or a small

number of attackers

Three lines of defense…

Page 56: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Lines of defense 1st line: Non-specific barriers

broad, external defense “walls & moats”

skin & mucous membranes 2nd line: Non-specific patrols

broad, internal defense “patrolling soldiers”

leukocytes = phagocytic WBC 3rd line: True immune system

specific, acquired immunity “elite trained units”

lymphocytes & antibodies B cells & T cells

Page 57: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

1st line: Non-specific External defense Barrier

skin

Traps mucous membranes, cilia,

hair, earwax

Elimination coughing, sneezing, urination, diarrhea

Unfavorable pH stomach acid, sweat, saliva, urine

Lysozyme enzyme digests bacterial cell walls tears, sweat

Lining of trachea: ciliated cells & mucus secreting cells

Page 58: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

2nd line: Non-specific defenses Patrolling cells & proteins

attack many pathogens, but don’t “remember” for next time leukocytes

phagocytic white blood cells macrophages, neutrophils, natural

killer cells

complement system proteins that destroy cells

inflammation increase in body temp. increase capillary permeability attract macrophages

fever

yeast

macrophage

bacteria

Page 59: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Discussion What are the advantages of the non-

specific defenses?

What are the disadvantages?

Page 60: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Specific defense with memory lymphocytes

B cells T cells

antibodies immunoglobulins

Responds to… antigens

cellular name tags specific pathogens specific toxins abnormal body cells (cancer)

3rd line: Acquired (active) ImmunityB cell

Page 61: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology“self” “foreign”

How are invaders recognized? Antigens

Peripheral proteins - what does that mean? cellular “name tag” proteins

“self” antigens no response from WBCs

“foreign” antigens response from WBCs pathogens: viruses, bacteria, protozoa, parasitic worms,

fungi, toxins non-pathogens: cancer cells, transplanted tissue, pollen

Page 62: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Specific Immune Response Two “pathways” of response Cell-mediated immunity

Call in specialist cells to target the pathogen!

Humoral immunity Use antibodies!

Cell-mediated and humoral pathways use a variety of white blood cells, or lymphocytes…

Page 63: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Lymphocytes B cells

mature in bone marrow humoral response system produce antibodies

T cells mature in thymus cellular response system

attack invaded cells

Macrophages Generalist cells from the 2nd

line of defense that can also interact with B and T cells in this 3rd line of defense, as you’ll see!

bone marrow

Page 64: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell-Mediated Immunity Step 1: A generalist

macrophage engulfs an invader, including its antigens

Step 2: The macrophage “presents” the invader’s antigens - basically, it pops them out of its own membrane! It becomes an antigen-

presenting cell

Page 65: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How is any cell tagged with antigens? Major histocompatibility (MHC) proteins

proteins which constantly carry bits of cellular material from the cytosol to the cell surface

“snapshot” of what is going on inside cell give the surface of cells a unique label or “fingerprint”

T or Bcell

MHC protein

MHC proteinsdisplaying self-antigens

Who goes there?self or foreign?

Page 66: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

How do T cells know a cell is infected? Infected cells digest some pathogens

MHC proteins carry pieces to cell surface foreign antigens now on cell membrane called Antigen Presenting Cell (APC)

macrophages can also serve as APC tested by Helper T cells

MHC proteins displaying foreign antigens

infectedcell

T cell with antigen receptors

TH cellWANTED

Page 67: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cell-Mediated Immunity Step 3: An immature T-cell binds to the antigen-

presenting cell; the presented antigens signal the T-cell, trigger it to: Release recruitment signals that, through signal

transduction, cause other immune cells to seek out and target that same antigen

Mature and proliferate into helper T-cells and cytotoxic T-cells

This is cell-to-cell signaling!

Page 68: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Helper T-Cells Signal cytotoxic T-cells and B-cells (humoral

immunity pathway, up next) to seek out and target that antigen Some become “memory T-cells,” which hang out

in the body, ready to immediately respond if that antigen ever returns!

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__t-cell_dependent_antigens__quiz_1_.html

Page 69: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Cytotoxic T-Cells

Killer T cellbinds toinfected

cell

Destroys infected body cells binds to target cell secretes perforin protein

punctures cell membrane of infected cell apoptosis

infected celldestroyed

cell membrane

Killer T cell

cell membrane

target cell

vesicle

perforin puncturescell membrane

Page 70: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Humoral Response Antibodies = Proteins that bind to a specific

antigen multi-chain proteins binding region matches molecular shape of antigens each antibody is unique & specific

millions of antibodies respond to millions of foreign antigens

tagging “handcuffs” “this is foreign…gotcha!”

each B cell has ~50,000 antibodies

Y

YY

YY

YY

Y

Y

YY

YY

YY

Y

Y

YY

YY

YY

Y

Y

YY

YYYY

Y

Y

Y

Y

Y

Y

Y

Y

YYY

Y

YY

Y Y

antigenantigen-binding site on antibody

variable binding region

Page 71: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

What do antibodies do to invaders?

macrophageeating tagged invaders

invading pathogens tagged with antibodiesY

Y

YY

YY

neutralize capture precipitate apoptosis

Page 72: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Humoral Response Step 1: If triggered by a helper T-cell, B

cells, upon encountering the antigen, bind to the pathogen that bears it

Step 2: The bound B-cell proliferates into two new kinds of B cells…

Page 73: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Humoral Respose Plasma B-Cells:

Produce antibodies against that antigen for a few days

Memory B-Cells: Long-lived, will rapidly proliferate into

fresh plasma cells for an instant counter-offensive if the antigen is ever re-encountered

Page 74: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Page 75: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Humoral Response The first ever encounter with the

pathogen = primary response (or primary immunity), moderately effective

Re-encounter in the future = secondary response. Immediate, powerful, decisive!

Page 76: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Discussion

Figure 12.19

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__the_immune_response.html

Use the conventions of cell signaling diagrams that we learned to construct a flowchart of specific immunity

events! Include both humoral and cell-mediated immunity in the same diagram.

Page 77: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Immune response

free antigens in blood antigens on infected cells

humoral response cellular response

B cells T cells

macrophages(APC)

helperT cells

plasmaB cells

memoryB cells

memoryT cells

cytotoxicT cells

YYY

Y

YY

Y

YantibodiesY Y Y

skinskin pathogen invasionantigen exposure

YY

Y

Y

YY

Y

YantibodiesY Y Y

alert alert

Page 78: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Vaccinations Immune system exposed

to harmless version of pathogen stimulates B cell system to produce

antibodies to pathogen rapid response on future exposure creates immunity

without getting disease!

Most successful against viruses

Page 79: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Human Immunodeficiency Virus virus infects helper T cells

AIDS: Acquired ImmunoDeficiency Syndrome AIDS itself doesn’t kill HIV-positive patients.

Discussion: If AIDS doesn’t kill HIV-positive patients, what does? What is the specific effect of infected T-cells? How does this alter cell-mediated immunity? Humoral immunity?

HIV & AIDS

Page 80: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology 2007-2008

Cell Signaling: Wrap-Up

Page 81: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Evolution of Homeostasis & Signaling Continuity of homeostatic mechanisms is a

means of studying shared ancestry A homeostatic mechanism can be thought of as

a “structure,” like an organ or a limb - it can show homology, analogy, vestigiality…

Changes to homeostatic mechanisms may occur in response to changes in environmental conditions Just like changes to a physical body structure!

Page 82: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Evolution of Homeostasis

For example, the control of blood osmolarity has been basically the same from flatworms through vertebrates Excretory demands haven’t changed

much, so neither has the control mechanism:

Page 83: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

osmoreceptors inhypothalamus

nephron

nephron

Blood Osmolarity

blood osmolarityblood pressure

ADH

increasedwater

reabsorption

increasethirst

renin

increasedwater & saltreabsorption

high

FeedbackEndocrine System Control

pituitary

angiotensinogenangiotensin

adrenalgland

aldosterone

JuxtaGlomerularApparatus

nephron(JGA)

low

Page 84: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Evolution of Homeostasis On the other hand, when environmental

demands change, so does the homeostatic mechanism that responds to them!

Consider control of blood oxygen. Water is liquid, low oxygen. Air is non-

liquid (and drying), high oxygen. So…

Page 85: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Discussion What parts of fish,

amphibian, and mammal control of blood oxygen are homologous? What are the differences?

Page 86: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Evolution of Homeostasis & Signaling

Correct and appropriate signaling mechanisms are under strong selective pressure A single simple change to a single

protein in a signaling pathway can have a massive effect, for better or for worse!

Page 87: AP Biology Cell Communication and Homeostasis AP Biology Dynamic Homeostasis

AP Biology

Signaling in Prokaryotes Signaling isn’t just for the multicellular! Prokaryotes signal to each other in quorum

sensing Example: Signals passed between neighboring

bacteria trigger the expression of genes for forming attachment surface proteins And the more bacteria you’re surrounded by, the

more and more of that signal you’re getting Discussion: What’s advantageous about that?